Abstract:

There is provided in the present invention a method for measuring a
distance between a lower end surface of a heat insulating member 14 and a
surface of a raw material melt 4 when a silicon single crystal is pulled
by a Czochralski method while a magnetic field is applied to a raw
material melt 4 in a crucible, a reference reflector 18 being located at
the lower end of the heat insulating member 14 which is located above the
surface of the raw material melt 4, characterized in that the method
includes steps of: actually measuring a distance A between the lower end
surface of the heat insulating member and the surface of the raw material
melt; observing a location R1 of a mirror image of the reference
reflector 18 reflected on the surface of the raw material melt by a
fixed-point observing apparatus 19; subsequently measuring a travel
distance B of the mirror image by the fixed-point observing apparatus 19
while pulling the silicon single crystal; and calculating the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt, from an actually measured value A and
the travel distance B of the mirror image. Thereby a method for measuring
a distance between a lower end surface of a heat insulating member and a
surface of a raw material melt which can stably and more accurately
measure the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt can be provided.

Claims:

1-10. (canceled)

11. A method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt when a
silicon single crystal is pulled up by a Czochralski method while a
magnetic field is applied to the raw material melt in a crucible, a
reference reflector being located at the lower end of the heat insulating
member which is located above the surface of the raw material melt,
wherein the method comprises at least steps of:actually measuring the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt;observing a location of a mirror
image of the reference reflector reflected on the surface of the raw
material melt by a fixed-point observing apparatus;subsequently measuring
a travel distance of the mirror image by the fixed-point observing
apparatus while pulling up the silicon single crystal; andcalculating the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt, from the actually measured value
and the travel distance of the mirror image.

12. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 11, wherein as the reference reflector, a reference reflector out
of any one of high-purity quartz, silicon and carbon is used.

13. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 11, wherein as the reference reflector, a reference reflector out
of high-purity white quartz or high-purity transparent quartz having a
whitened surface is used.

14. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 11, wherein a projection which is longer than the reference
reflector and which has a known length is provided at the lower end of
the heat insulating member; the projection is contacted with the surface
of the raw material melt by raising the crucible so as to actually
measure the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt when the distance between
the lower end surface of the heat insulating member and the surface of
the raw material melt is actually measured.

15. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 12, wherein a projection which is longer than the reference
reflector and which has a known length is provided at the lower end of
the heat insulating member; the projection is contacted with the surface
of the raw material melt by raising the crucible so as to actually
measure the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt when the distance between
the lower end surface of the heat insulating member and the surface of
the raw material melt is actually measured.

16. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 13, wherein a projection which is longer than the reference
reflector and which has a known length is provided at the lower end of
the heat insulating member; the projection is contacted with the surface
of the raw material melt by raising the crucible so as to actually
measure the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt when the distance between
the lower end surface of the heat insulating member and the surface of
the raw material melt is actually measured.

17. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 14, wherein as the projection, a projection out of any one of
quartz, silicon and carbon is used.

18. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 11, wherein a lower end of a seed crystal for growing the silicon
single crystal is detected by an apparatus for detecting a reference
location arranged above the raw material melt so as to give the location
as a reference location; subsequently the lower end of the seed crystal
is lowered between the lower end of the reference reflector and the
surface of the raw material melt; the lower end of the seed crystal is
contacted with the surface of the raw material melt by raising the
crucible so as to actually measure the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt based on the distance between the contact location and the reference
location as well as the distance between the lower end surface of the
heat insulating member and the reference location when the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt is actually measured.

19. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 12, wherein a lower end of a seed crystal for growing the silicon
single crystal is detected by an apparatus for detecting a reference
location arranged above the raw material melt so as to give the location
as a reference location; subsequently the lower end of the seed crystal
is lowered between the lower end of the reference reflector and the
surface of the raw material melt; the lower end of the seed crystal is
contacted with the surface of the raw material melt by raising the
crucible so as to actually measure the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt based on the distance between the contact location and the reference
location as well as the distance between the lower end surface of the
heat insulating member and the reference location when the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt is actually measured.

20. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 13, wherein a lower end of a seed crystal for growing the silicon
single crystal is detected by an apparatus for detecting a reference
location arranged above the raw material melt so as to give the location
as a reference location; subsequently the lower end of the seed crystal
is lowered between the lower end of the reference reflector and the
surface of the raw material melt; the lower end of the seed crystal is
contacted with the surface of the raw material melt by raising the
crucible so as to actually measure the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt based on the distance between the contact location and the reference
location as well as the distance between the lower end surface of the
heat insulating member and the reference location when the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt is actually measured.

21. The method for measuring a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt according to
claim 11, wherein a central magnetic field intensity of the applied
magnetic field is a horizontal magnetic field of 300 G to 7000 G.

22. A method for controlling a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt, wherein the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt measured by the method for measuring
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt according to claim 11 is fed
back while pulling the silicon single crystal; and the crucible or the
heat insulating member is moved such that the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt takes a setting value.

23. A method for controlling a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt, wherein the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt measured by the method for measuring
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt according to claim 12 is fed
back while pulling the silicon single crystal; and the crucible or the
heat insulating member is moved such that the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt takes a setting value.

24. A method for controlling a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt, wherein the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt measured by the method for measuring
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt according to claim 13 is fed
back while pulling the silicon single crystal; and the crucible or the
heat insulating member is moved such that the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt takes a setting value.

25. A method for controlling a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt, wherein the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt measured by the method for measuring
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt according to claim 14 is fed
back while pulling the silicon single crystal; and the crucible or the
heat insulating member is moved such that the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt takes a setting value.

26. A method for controlling a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt, wherein the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt measured by the method for measuring
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt according to claim 17 is fed
back while pulling the silicon single crystal; and the crucible or the
heat insulating member is moved such that the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt takes a setting value.

27. A method for controlling a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt, wherein the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt measured by the method for measuring
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt according to claim 18 is fed
back while pulling the silicon single crystal; and the crucible or the
heat insulating member is moved such that the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt takes a setting value.

28. A method for controlling a distance between a lower end surface of a
heat insulating member and a surface of a raw material melt, wherein the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt measured by the method for measuring
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt according to claim 21 is fed
back while pulling the silicon single crystal; and the crucible or the
heat insulating member is moved such that the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt takes a setting value.

29. A method for manufacturing a silicon single crystal, wherein the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt is controlled by the method for
controlling the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt according to
claim 22 so as to manufacture the silicon single crystal.

30. The method for manufacturing a silicon single crystal according to
claim 29, wherein the manufactured silicon single crystal is defect-free
on the entire plane in the radial direction.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a method for measuring a distance
between a lower end surface of a heat insulating member arranged above a
surface of a raw material melt and the surface of the raw material melt
when a single crystal is pulled by a Czochralski method from the raw
material melt in a crucible, and also relates to a method for controlling
the distance.

BACKGROUND ART

[0002]As a method for manufacturing a silicon single crystal used for
manufacturing a semiconductor device, a Czochralski method (CZ method)
for growing and at the same time pulling a silicon single crystal from a
raw material melt in a quartz crucible is widely performed. In a CZ
method, a seed crystal is dipped in a raw material melt (a silicon melt)
in a quartz crucible in an inert gas atmosphere, and then both the quartz
crucible and the seed crystal are rotated and at the same time the seed
crystal is pulled so as to grow a silicon single crystal of a desired
diameter.

[0003]In recent years, grown-in defect in a silicon wafer becomes a
problem due to the development of high integration and the resulting
miniaturization of semiconductor devices. Crystal defect is a factor
degrading characteristics of semiconductor devices, and influences more
increasingly with the development of miniaturization of a device. As such
a grown-in defect, octahedral void-state defect, which is an aggregate of
vacancies in the silicon single crystal produced by a CZ method (See
Analysis of side-wall structure of grown-in twin-type octahedral defects
in Czochralski silicon, Jpn. J. Appl. Phys. Vol. 37 (1998) p-p.
1667-1670), a dislocation cluster formed as an aggregate of interstitial
silicon (See Evaluation of micro defects in as-grown silicon crystals,
Mat. Res. Soc. Symp. Proc. Vol. 262 (1992) p-p 51-56) and the like are
known.

[0004]It is shown that the introduced amount of each of these grown-in
defects is determined by temperature gradient of the crystal on its
growing interface and the growth rate of the silicon single crystal. (See
the mechanism of swirl defects formation in silicon, Journal of Crystal
growth, 1982, p-p 625-643.) As methods for manufacturing a low-defect
silicon single crystal utilizing this principle, publication of
Unexamined Japanese Patent Application No. H6-56588, for example,
discloses a method slowing the growth rate of the silicon single crystal,
while publication of Unexamined Japanese Patent Application No. H7-257991
discloses a method for pulling the silicon single crystal at a rate not
exceeding the maximum pulling rate which is approximately proportional to
the temperature gradient of the boundary region between the solid phase
and the liquid phase of the silicon single crystal. Other methods such as
an improved CZ method in which the temperature gradient (G) and growth
rate (V) during the crystal growth are focused (See "Japanese Association
for Crystal Growth", vol. 25, No. 5, 1998) are also reported. It is thus
necessary to control highly precisely the temperature gradient of the
crystal.

[0005]In these methods, a structure (heat insulating member) for
insulating radiant heat in a form of a cylinder or an inverted cone is
provided around the silicon single crystal to be grown above the melt
surface so as to control the temperature gradient of the crystal. Since
the temperature gradient of the crystal at a high temperature of the
crystal can be thereby increased, it is advantageous for obtaining a
defect-free crystal at a high speed. In order to control accurately the
temperature gradient of the crystal, however, the distance between the
surface of the raw material melt and the lower end surface of the heat
insulating member located above the surface of the raw material melt
(hereinafter, sometimes referred to as DPM) is necessary to be controlled
highly precisely to be a predetermined distance. It has been difficult
with a conventional method, however, to control the DPM precisely such
that the DPM is the predetermined distance.

[0006]In addition, as the crystal diameter increases, the location of the
melt surface varies very much depending on the weight (varying
thickness), deformation during operation and expansion of the quartz
crucible, so that the location of the melt surface varies per batch of
the crystal growth, which is a problem. Therefore, it becomes more
difficult to control the interval between the melt surface and the heat
insulating member precisely such that the interval is a predetermined
interval.

[0007]In order to improve these problems, it is proposed in publication of
Unexamined Japanese Patent Application No. H6-116083, for example, to
provide a reference reflector in a CZ furnace and to measure a relative
distance between a real image of the reference reflector and a mirror
image of the reference reflector reflected on the melt surface so as to
measure the distance between the reference reflector and the melt
surface. This method is for precisely controlling the interval between
the melt surface and the heat insulating member based on the measurement
result such that the interval is a predetermined interval.

[0008]Furthermore, publication of Unexamined Japanese Patent Application
No. 2001-342095 discloses a method in which curve of the raw material
melt due to the rotation of the crucible is considered in order to obtain
the stability of the mirror image of the reference reflector.

[0009]In these methods, the real image of the reference reflector and the
mirror image of the reference reflector are captured by a detecting means
such as an optical camera or the like. The brightness of the captured
real and mirror images of the reference reflector is quantized to two
levels (binarization process) by determining a constant threshold
(threshold for binarization level). In other words, a brighter location
and a darker location than the threshold for binarization level are
distinguished. Then by measuring where the edge is located and by
converting the measured value, the distance between the real image and
the mirror image is measured.

[0010]However, there is a problem that the distance between the reference
reflector and the melt surface cannot be stably and accurately measured
since the brightness of the mirror image of the reference reflector
reflected on the melt surface is changed over the time period of the
crystal growth process and as a result a detection value by the optical
camera before the binarization varies, or since a noise which is not a
mirror image of the reference reflector such as a splash of melt attached
to a structural part in the CZ furnace is detected.

[0011]As an another problem, if a raw material melt is contained in a
quartz crucible having a bore diameter of 800 mm or more, and a silicon
single crystal having a diameter of 300 mm or more is manufactured
without applying a magnetic field, the melt surface is fluctuated, so
that an accurate location of the melt surface cannot be stably detected.
A relative distance between the reference reflector and the melt surface
cannot be measured stably and accurately in this case either.

[0012]If the measuring result of the relative distance between the
reference reflector and the melt surface is inaccurate, the interval
between the melt surface and the heat insulating member cannot be
controlled precisely to be a determined interval. As a result, a silicon
single crystal with a desired quality cannot be manufactured with
preferable productivity.

DISCLOSURE OF THE INVENTION

[0013]The present invention has been made in view of the above-mentioned
problems, and an object of the present invention is to provide a
measuring method for measuring stably and more accurately the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt. Another object of the present invention
is to manufacture a high-quality silicon single crystal with a
free-defect region precisely by utilizing this measuring method in order
to manufacture the silicon single crystal.

[0014]In order to achieve the above-mentioned objects, the present
invention provides a method for measuring a distance between a lower end
surface of a heat insulating member and a surface of a raw material melt
when a silicon single crystal is pulled by a Czochralski method while a
magnetic field is applied to the raw material melt in a crucible, a
reference reflector being located at the lower end of the heat insulating
member which is located above the surface of the raw material melt,
characterized in that the method comprises at least steps of: actually
measuring the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt; observing a
location of a mirror image of the reference reflector reflected on the
surface of the raw material melt by a fixed-point observing apparatus;
subsequently measuring a travel distance of the mirror image by the
fixed-point observing apparatus while pulling the silicon single crystal;
and calculating the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt, from the
actually measured value and the travel distance of the mirror image.

[0015]As mentioned above, in the present invention, the silicon single
crystal is pulled while a magnetic field is applied. Since convection of
the raw material melt is thereby suppressed and as a result waviness of
front surface of the raw material melt can be suppressed, the melt
surface becomes like mirror plane even while pulling the silicon single
crystal, so that the mirror image of the reference reflector can be
observed easily, and the distance between the lower end surface of the
heat insulating member and the surface of the raw material melt can be
stably and accurately measured.

[0016]Furthermore, in the present invention, the distance between the
lower end surface of the heat insulating member and the surface of the
raw material melt is actually measured first by using a mechanical method
or the like, and a location of the mirror image of the reference
reflector reflected on the surface of the raw material melt is observed
using a fixed-point observing apparatus. Subsequently, during pulling the
silicon single crystal, the travel distance of the mirror image is
measured by the fixed-point observing apparatus. By calculating the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt being pulled from the actually
measured value and the travel distance of the mirror image, the measuring
range by the image observation is further limited, so that with
observational error being reduced, the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt can be measured precisely and accurately during pulling the silicon
single crystal.

[0017]Here, the "reference reflector" in the preset invention is a body
arranged at the lower end of the heat insulating member, and its mirror
image is reflected on the surface of the raw material melt. By observing
this mirror image, the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt can be
calculated and the location of the surface of the raw material melt can
be controlled.

[0018]Here, as the reference reflector, a reference reflector out of any
one of high-purity quartz, silicon and carbon is preferably used.

[0019]By thus using a reference reflector out of any one of high-purity
quartz, silicon and carbon as the reference reflector mounted at the
lower end of the heat insulating member, there is only slight risk that
the reference reflector may contaminate a growing silicon single crystal
with impurities. Thereby a high-quality silicon single crystal can be
grown.

[0020]Additionally, as the reference reflector, a reference reflector out
of high-purity white quartz or high-purity transparent quartz having a
whitened surface is preferably used.

[0021]By thus using a reference reflector out of high-purity white quartz
or high-purity transparent quartz having a whitened surface as the
reference reflector mounted at the lower end of the heat insulating
member, there is no risk that the silicon single crystal may be
contaminated with particles due to the degradation of the reference
reflector during pulling the silicon single crystal. In addition, since
the reference reflector is white, visibility of mirror images on the
surface of the raw material melt is improved, and the observation of
mirror images can be achieved more accurately, so that a silicon single
crystal with high purity and a high quality can be grown.

[0022]Furthermore, in the present invention, when the distance between the
lower end surface of the heat insulating member and the surface of the
raw material melt is actually measured, a projection which is longer than
the reference reflector and which has a known length is provided at the
lower end of the heat insulating member; the projection is contacted with
the surface of the raw material melt by raising the crucible so as to
allow the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt to be actually measured.

[0023]By thus providing a projection which is longer than the reference
reflector and which has a known length at the lower end of the heat
insulating member; contacting the projection with the surface of the raw
material melt by raising the crucible so as to actually measure the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt, since the length of the projection
is known, the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt can be
actually measured with a simple operation. In addition, since the
projection is longer than the reference reflector, there is no risk that
the raw material melt may be attached to the reference reflector, when
the crucible is raised so as to contact the projection with the surface
of the raw material melt.

[0024]As the projection, a projection out of any one of quartz, silicon
and carbon is preferably used.

[0025]By thus using a projection out of any one of quartz, silicon and
carbon as the projection provided at the lower end of the heat insulating
member, even if the projection, which is contacted with the raw material
melt, is melt in the raw material melt for example, there is only slight
risk that the raw material melt is contaminated with impurities, so that
a high-quality silicon single crystal can be grown.

[0026]Furthermore, in the present invention, when the distance between the
lower end surface of the heat insulating member and the surface of the
raw material melt is actually measured, a lower end of a seed crystal for
growing the silicon single crystal is detected by an apparatus for
detecting a reference location arranged above the raw material melt so as
to give the location as a reference location; subsequently the lower end
of the seed crystal is lowered between the lower end of the reference
reflector and the surface of the raw material melt; the lower end of the
seed crystal is contacted with the surface of the raw material melt by
raising the crucible so as to actually measure the distance between the
lower end surface of the heat insulating member and the surface of the
raw material melt based on the distance between the contact location and
the reference location as well as the distance between the lower end
surface of the heat insulating member and the reference location.

[0027]By thus detecting the lower end of the seed crystal for growing the
silicon single crystal by an apparatus for detecting a reference location
arranged above the raw material melt so as to give the location as a
reference location; subsequently lowering the lower end of the seed
crystal between the lower end of the reference reflector and the surface
of the raw material melt; contacting the lower end of the seed crystal
with the surface of the raw material melt by raising the crucible so as
to actually measure the distance between the lower end surface of the
heat insulating member and the surface of the raw material melt based on
the distance between the contact location and the reference location as
well as the distance between the lower end surface of the heat insulating
member and the reference location, the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt can be actually measured by a simple operation. In addition, since
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt is actually measured by means of
a seed crystal, there is only slight risk of the raw material melt being
contaminated with impurities, so that a high-quality silicon single
crystal can be grown. Furthermore, by lowering the lower end of the seed
crystal between the lower end of the reference reflector and the surface
of the raw material melt, when the lower end of the seed crystal is
contacted with the surface of the raw material melt by raising the
crucible, there is no risk that the raw material melt is attached to the
reference reflector.

[0028]It is preferable in the present invention that a central magnetic
field intensity of the applied magnetic field is a horizontal magnetic
field of 300 G to 7000 G.

[0029]Since by thus setting the central magnetic field intensity of the
applied magnetic field during measurement to be a horizontal magnetic
field of 300 G to 7000 G, the surface of the raw material melt is hardly
fluctuated, fluctuation of the mirror image reflected on the surface of
the raw material melt can be suppressed, so that the location of the
surface of the raw material melt can be stabilized, and consequently the
travel distance of the mirror image can be more accurately measured.

[0030]There is also provided in accordance with the present invention, a
method for controlling a distance between a lower end surface of a heat
insulating member and a surface of a raw material melt, characterized in
that the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt measured by the
above-mentioned method for measuring the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt is fed back while pulling the silicon single crystal; and the
crucible or the heat insulating member is moved such that the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt takes a setting value.

[0031]As mentioned above, the distance between the lower end surface of
the heat insulating member and the surface of the raw material melt
measured by the above-mentioned method for measuring the distance between
the lower end surface of the heat insulating member and the surface of
the raw material melt is fed back while pulling the silicon single
crystal; and the crucible or the heat insulating member is moved such
that the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt takes a setting value.
Since the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt can be thereby measured
more stably and more accurately, the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt can be controlled highly precisely if the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt is controlled based on this measurement result.

[0032]There is provided in the present invention a method for
manufacturing a silicon single crystal, characterized in that a distance
between a lower end surface of a heat insulating member and a surface of
a raw material melt is controlled by the above-mentioned method for
controlling the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt so as to
manufacture a silicon single crystal.

[0033]Since by thus manufacturing the silicon single crystal by the
above-mentioned controlling method, the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt can be controlled highly precisely, the temperature gradient of the
crystal axis in the direction of the crystal growth axis can be
controlled extremely precisely, so that a high-quality silicon single
crystal can be manufactured efficiently and with high productivity.

[0034]Furthermore, the above-mentioned method for manufacturing a silicon
single crystal is a method where the manufactured silicon single crystal
can be defect-free on the entire plane in the radial direction.

[0035]By thus using the above-mentioned method for measuring the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt in a method for manufacturing a silicon
single crystal, a defect-free silicon single crystal on the entire plane
in the radial direction can be pulled.

[0036]As mentioned above, in accordance with a method for measuring the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt according to the present invention,
the distance between the lower end surface of the heat insulating member
and the surface of the raw material melt can be measured more stably and
more accurately. By controlling the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt based on the measurement result, the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt can be controlled highly precisely. Therefore, the temperature
gradient of the crystal axis in the direction of the crystal growth axis
can be controlled extremely precisely, so that a high-quality silicon
single crystal can be manufactured efficiently and with high
productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is a view illustrating a method for measuring the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt in accordance with the present
invention, where FIG. 1(a) is a view illustrating the movement of the
surface of the raw material melt and locational relationship of each
member and FIG. 1(b) is a schematic view of images obtained by a
fixed-point observing apparatus;

[0038]FIG. 2 is a schematic view illustrating a method for measuring the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt when a silicon single crystal is
pulled in accordance with the present invention;

[0039]FIG. 3 is a view illustrating a method for actually measuring the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt, where FIG. 3(a) shows the method in
a case of using a projection and FIG. 3(b) shows the method in a case of
using a seed crystal;

[0040]FIG. 4 is a view showing measured values of DPM measured by a DPM
measuring method in accordance with the present invention and setting
values of DPM (with respect to Examples 1 and 2);

[0041]FIG. 5 is a schematic view illustrating a silicon single crystal
obtained by controlling the DPM as in FIG. 4;

[0042]FIG. 6 is a view showing measured values of DPM measured by a
conventional DPM measuring method and setting values of DPM (Comparative
Example); and

[0043]FIG. 7 is a schematic view illustrating a silicon single crystal
obtained by controlling the DPM as in FIG. 6.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0044]Hereinbelow, the present invention is described more in detail.

[0045]As mentioned above, conventionally a reference reflector is provided
in a CZ furnace and by measuring a relative distance between a real image
of the reference reflector and a mirror image of the reference reflector
reflected on the melt surface, the distance between the reference
reflector and the melt surface is measured. The measurement is performed
such that the real image of the reference reflector and the mirror image
of the reference reflector are captured by a detecting means such as an
optical camera or the like, and then brightness of the captured real and
mirror images of the reference reflector is quantized to two output
levels (binarization process) by determining a constant threshold
(threshold for binarization level).

[0046]However, there is a problem that the distance between the reference
reflector and the melt surface cannot be stably and accurately measured
since the brightness of the mirror image of the reference reflector
reflected on the melt surface is changed over the time period of the
crystal growth process and as a result a detection value by the optical
camera before the binarization varies, or since a noise which is not a
mirror image of the reference reflector such as a splash of melt attached
to a structural part in the CZ furnace is detected.

[0047]As an another problem, if a silicon single crystal having a diameter
of 300 mm or more is manufactured, for example, the melt surface is
fluctuated, so that an accurate location of the melt surface cannot be
stably detected.

[0048]If the measurement result of the relative distance between the
reference reflector and the melt surface is thus inaccurate, an interval
between the melt surface and the heat insulating member cannot be
controlled precisely to be a predetermined interval. As a result a
silicon single crystal with a desired quality cannot be manufactured with
good productivity.

[0049]The inventors of the present invention have diligently studied and
examined in order to solve these problems, have accordingly found that in
order to more stably and more correctly measure the distance between the
lower end surface of a heat insulating member and the surface of the raw
material melt, a silicon single crystal is pulled while a magnetic field
being applied, the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt is actually
measured; subsequently a travel distance of a mirror image is measured by
a fixed-point observing apparatus while pulling the silicon single
crystal; and the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt is calculated,
from the actually measured value and the travel distance of the mirror
image so as to measure the distance between the lower end surface of a
heat insulating member and the surface of the raw material melt, and have
thereby completed the present invention.

[0050]Hereinbelow, embodiments of the present invention are described in
reference to the drawing, though the present invention is not limited to
them.

[0051]FIG. 1 is a view illustrating a method for measuring the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt in accordance with the present
invention, where FIG. 1(a) is a view illustrating the movement of the
surface of the raw material melt and locational relationship of each
member, and FIG. 1(b) is a schematic view of images obtained by a
fixed-point observing apparatus. FIG. 2 is a schematic view illustrating
a method for measuring the distance between the lower end surface of the
heat insulating member and the surface of the raw material melt when a
silicon single crystal is pulled in accordance with the present
invention.

[0052]Before a silicon single crystal 3 is pulled by a Czochralski method
during applying a magnetic field to a raw material melt 4 in a crucible
as shown in FIG. 2, a reference reflector 18 is provided at the lower end
of a heat insulating member 14 located above the raw material melt 4 as
shown in FIG. 1(a). Then a distance A between the lower end of the heat
insulating member 14 and the front surface of the raw material melt 4 is
actually measured, and location of a mirror image R1 of the reference
reflector 18 reflected on the surface of the raw material melt is
observed by a fixed-point observing apparatus 19. Subsequently, while
pulling of the silicon single crystal 3, a travel distance B of the
mirror image is measured by the fixed-point observing apparatus 19, so
that the distance between the lower end surface of the heat insulating
member and the surface of the raw material melt is calculated from the
actually measured value A and the travel distance B of the mirror image.

[0053]By thus actually measuring the distance between the lower end
surface of the heat insulating member 14 and the front surface of the raw
material melt 4; by observing a location of the mirror image of the
reference reflector reflected on the surface of the raw material melt
using the fixed-point observing apparatus; subsequently during pulling
the silicon single crystal by measuring the travel distance of the mirror
image by the fixed-point observing apparatus; and by calculating the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt from the actually measured value and
the travel distance of the mirror image, the measuring range by the image
observation is further limited, so that with observational error by the
fixed-point observing apparatus being reduced, the distance between the
lower end surface of the heat insulating member and the surface of the
raw material melt can be measured precisely and accurately during pulling
the silicon single crystal.

[0054]In addition, by pulling the silicon single crystal while the
magnetic field is applied, convection of the raw material melt can be
suppressed and as a result waviness of front surface of the raw material
melt can be suppressed, so that the melt surface becomes like mirror
plane even while pulling the silicon single crystal. Consequently, the
mirror image of the reference reflector can be observed easily, and the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt can be stably and accurately
measured.

[0055]When the reference reflector 18 is provided at the lower end of the
heat insulating member 14 located above the raw material melt 4 as shown
in FIG. 1(a), as the reference reflector 18, a reference reflector out of
any one of high-purity quartz, silicon and carbon is preferably used.

[0056]By employing a reference reflector made of such a material, there is
only slight risk that the reference reflector 18 may contaminate a
growing silicon single crystal 3 with impurities, so that a high-quality
silicon single crystal 3 can be grown.

[0057]Additionally, as the reference reflector 18, a reference reflector
out of high-purity white quartz or high-purity transparent quartz having
a whitened surface is especially preferably used.

[0058]By thus using a reference reflector out of high-purity white quartz
or high-purity transparent quartz having a whitened surface as the
reference reflector 18 mounted at the lower end of the heat insulating
member 14, there is no risk that the silicon single crystal 3 may be
contaminated with particles due to the degradation of the reference
reflector 18 during pulling the silicon single crystal 3.

[0059]As a material for the heat insulating member 14 or the like arranged
above the raw material melt 4, graphite material is often employed. When
travel of the mirror image is observed by the fixed-point observing
apparatus 19, since the graphite material is reflected on the front
surface of the silicon melt 4, and since the reference reflector 18 is
white, in a case that a reference reflector out of high-purity white
quartz or high-purity transparent quartz having a whitened surface is
used as the reference reflector 18, visibility of mirror images on the
surface of the raw material melt 4 observed by the fixed-point observing
apparatus 19 is improved, and the observation of mirror images can be
achieved more accurately, so that the silicon single crystal 3 with high
purity and a high quality can be grown.

[0060]As for examples actually measuring the distance A between the lower
end of the heat insulating member 14 and the front surface of the raw
material melt 4, two embodiments such as those shown in FIG. 3(a) and
FIG. 3(b) can be mentioned.

[0061]FIG. 3 is a view illustrating a method for actually measuring the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt, where FIG. 3(a) shows a case of
using a projection and FIG. 3(b) shows a case of using a seed crystal.

[0062]As shown in FIG. 3(a), when the distance A between the lower end of
the heat insulating member 14 and the front surface of the raw material
melt 4 is actually measured using a projection, a projection 17 which is
longer than the reference reflector 18 and which has a known length is
provided at the lower end of the heat insulating member 14, and the
projection 17 is contacted with the raw material melt 4 by raising the
crucible.

[0063]If the distance A between the lower end of the heat insulating
member 14 and the front surface of the raw material melt 4 is thus
actually measured, since the length of the projection 17 is known, the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt can be actually measured by a simple
operation. Since the projection is longer than the reference reflector,
there is no risk of the raw material melt being attached to the reference
reflector, when the projection is contacted with the surface of the raw
material melt by raising the crucible.

[0064]In order to detect the contact between the projection 17 and the raw
material melt 4, as shown in FIG. 3(a), a gas flow-guide cylinder 13 to
which the heat insulating member 14 is mounted, the heat insulating
member 14 and the projection 17 are electrically connected, and a
crucible axis 15 which holds the crucible filled with the raw material
melt 4 and the gas flow-guide cylinder 13 are electrically connected by
an actual measurement apparatus 20.

[0065]Consequently, when the crucible is raised and the raw material melt
4 is contacted with the projection 17, the actual measurement apparatus
20 detects it electrically. The location of the crucible at this time is
recorded. At this location of the crucible, in other words, at the
location of the surface of the raw material melt, the distance between
the lower end surface of the heat insulating member and the surface of
the raw material melt matches with the length of the projection, so that
the distance A between the lower end surface of the heat insulating
member and the surface of the raw material melt can be actually measured.

[0066]As the projection 17, a projection out of any one of quartz, silicon
and carbon is preferably used. Silicon is especially more preferable from
the viewpoints of electrical resistance and impurity contamination.

[0067]By employing the projection 17 out of such material, even if the
projection 17 is melt in the raw material melt 4 when contacted with the
raw material melt 4, for example, there is only slight risk that the raw
material melt 4 is contaminated with impurities, so that a high-quality
silicon single crystal can be grown.

[0068]If the raw material melt is silicon, silicon, which is the same
material, is especially preferably used as a material of the projection
17.

[0069]Next, the case using a seed crystal as shown in FIG. 3(b) when the
distance A between the lower end of the heat insulating member 14 and the
front surface of the raw material melt 4 is actually measured is
described. By detecting the lower end of a seed crystal 12 for growing
the silicon single crystal 3 by an apparatus for detecting a reference
location 24 arranged above the raw material melt 4 (at a pulling chamber
for example), giving the location as a reference location; subsequently
lowering the lower end of the seed crystal 12 between the lower end of
the reference reflector 18 and the surface of the raw material melt 4.
Here the lower end of the seed crystal 12 is stopped at a location of the
raw material melt surface corresponding with a desired DPM when the
crucible is raised so as to contact with the raw material melt 4. Then
the crucible is raised so as to contact the lower end of the seed crystal
12 with the raw material melt 4.

[0070]Based on the distance between this contact location and the
reference location as well as a known distance between the lower end
surface of the heat insulating member and the reference location, the
distance A between the lower end surface of the heat insulating member
and the surface of the raw material melt can be actually measured.

[0071]By thus using the seed crystal so as to actually measure the
distance A between the lower end surface of the heat insulating member
and the surface of the raw material melt, the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt can be actually measured by a simple operation.
Additionally, since the distance between the lower end surface of the
heat insulating member and the surface of the raw material melt is
actually measured with a seed crystal, there is also only slight risk of
the raw material melt being contaminated with impurities, so that a
high-quality silicon single crystal can be grown. Furthermore, by
lowering the lower end of the seed crystal between the lower end of the
reference reflector and the surface of the raw material melt, there is no
risk that the raw material melt is attached to the reference reflector
when the seed crystal is contacted with the surface of the raw material
melt by raising the crucible.

[0072]In order to detect the contact of the seed crystal 12 and the raw
material melt 4, a wire 23 hanging the seed crystal 12 and the crucible
axis 15 which holds the crucible filled with the raw material melt 4 are
electrically connected by an actual measurement apparatus 20 as shown in
FIG. 3(b).

[0073]Then, when the crucible is raised and the raw material melt 4 is
contacted with the seed material 12, the actual measurement apparatus 20
detects it electrically. The location of the crucible at this time is
recorded. At this location of the crucible, in other words, at this
location of the surface of the raw material melt, the distance between
the lower end surface of the heat insulating member and the surface of
the raw material melt can be actually measured.

[0074]Simultaneously with the distance A between the lower end of the heat
insulating member 14 and the front surface of the raw material melt 4
being actually measured by the above-mentioned method, the location of an
mirror image R1 of the reference reflector reflected on the surface of
the raw material melt is observed by the fixed-point observing apparatus
19.

[0075]Next, the silicon single crystal 3 is pulled using an apparatus
shown in FIG. 2. This apparatus for manufacturing a silicon single
crystal 40 is equipped with a main chamber 1 containing members such as a
quartz crucible 5, a pulling chamber 2 continuously arranged above to the
main chamber 1, the heat insulating member 14 for controlling the
temperature gradient of the crystal, a heater 7 for heating and melting
polycrystalline silicon material, a graphite crucible 6 out of graphite
holding the quartz crucible 5, a heat insulator 8 for preventing the heat
from the heater 7 from being directly radiated to the main chamber 1, the
wire 23 for pulling the silicon single crystal, the crucible axis 15 for
holding the crucibles 5 and 6, and a control apparatus 22 for controlling
the crucible location.

[0076]The manufacturing apparatus 40 like this allows the silicon single
crystal 3 to be pulled as follows. Before actually measuring the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt, polycrystalline silicon material with
high purity is contained in the quartz crucible 5 in advance, the
material is heated and melt to melting point of silicon (about
1420° C.) or more by the heater 7 arranged around the graphite
crucible 6 so as to prepare the raw material melt 4.

[0077]Then, as described above, the distance between the lower end of the
heat insulating member 14 and the front surface of the raw material melt
4 is actually measured, and the location of the mirror image R1 of the
reference reflector reflected on the surface of the raw material melt is
observed by the fixed-point observing apparatus 19.

[0078]In a case that the distance between the lower end surface of the
heat insulating member and the surface of the raw material melt is
actually measured by using a projection as shown in FIG. 3(a), the
location of the crucible is lowered until a desired DPM is obtained.
Then, after the seed crystal 12 is contacted with the raw material melt
4, the pulling wire 23 is wound gently by a (not shown) reel mechanism, a
neck portion is formed, and then the crystal diameter is increased so as
to grow a portion having a constant diameter.

[0079]Here, the silicon single crystal 3 is pulled during applying a
magnetic field to the raw material melt by a magnet 16. The central
magnetic field intensity (central magnetic field intensity of the line
connecting coil centers) of the magnetic filed being applied is
especially preferable a horizontal magnetic field of 300 G to 7000 G. By
setting such a magnetic field intensity, since the surface of the raw
material melt is hardly fluctuated, the fluctuation of the mirror image
reflected on the surface of the raw material melt can be suppressed, so
that the location of the surface of the raw material melt can be
stabilized, and consequently the travel distance of the mirror image can
be more accurately measured.

[0080]Next, a method for measuring the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt while pulling the silicon single crystal 3 is described. The
location of the mirror image of the reference reflector 18 is moved from
that of the mirror image R1 of the reference reflector 18 reflected on
the raw material melt captured by the fixed-point observing apparatus 19
before pulling the silicon single crystal, to the location of the mirror
image R2 of the reference reflector 18 when the silicon single crystal is
pulled and the surface of the raw material melt is lowered.

[0081]Here, the travel distance B of the mirror image from the location R1
to the location R2 is converted to the travel distance C of the surface
of the raw material melt by means of a measurement calculation apparatus
21 connected to the fixed-point observing apparatus 19. This conversion
can be performed geometrically by calculating from the location and angle
of the fixed-point observing apparatus 19 and the like as follows:

B=2C sin θ

where the travel distance of the raw material melt is given as C, the
travel distance of the mirror image is given as B, and the reflection
angle of the mirror image is given as θ. Thus, the travel distance
C of the raw material melt can be evaluated from the travel distance B of
the mirror image obtained by the fixed-point observing apparatus 19, and
the DPM in a case of the mirror image being in a location R2 can be
evaluated by adding the actually measured value A to the travel distance
C of the raw material melt.

[0082]Here, if θ≧30°, then C<B, so that a slight
travel of the raw material melt can be measured by enlarging it by the
travel of the mirror image.

[0083]In order to calculate the DPM more accurately, however, conversion
coefficient may be evaluated in advance from the travel distance B of the
mirror image observed before the silicon single crystal is pulled,
specifically when the crucible location, i.e., the surface of the raw
material melt is lowered by 20 mm, for example.

[0084]Though the fixed-point observing apparatus 19 is not specifically
limited, an optical camera (such as a CCD camera), which is generally
used, can be mentioned as an example.

[0085]By thus setting and by only capturing the travel distance B of the
mirror image by means of the fixed-point observing apparatus 19 while
pulling the silicon single crystal, the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt can be precisely calculated from the actually measured value A of
the DPM before pulling the silicon single crystal and the travel distance
C of the surface of the raw material melt calculated from the travel
distance B of the mirror image.

[0086]The actually measured value A of the DPM before pulling the silicon
single crystal can be calculated by the control apparatus 22 for
controlling the crucible location.

[0087]Next, in order to control the distance between the lower end surface
of the heat insulating member and the surface of the raw material melt,
the travel distance of the mirror image is always observed while pulling
the silicon single crystal, and the distance between the lower end
surface of the heat insulating member and the surface of the raw material
melt measured by the above-mentioned method for measuring the distance
between the lower end surface of the heat insulating member and the
surface of the raw material melt is fed back as needed. The crucible 5
and 6 or the heat insulating member 14 are preferably moved such that the
distance between the lower end surface of the heat insulating member and
the surface of the raw material melt takes a setting value. The crucible
axis 15 may be moved up or down in order to move the crucible, while the
gas flow-guide cylinder may be moved up or down by a travel mechanism 25
for the gas flow-guide cylinder in order to move the heat insulating
member.

[0088]By thus feeding back the DPM measurement value while pulling the
silicon single crystal, and by moving the crucible or the heat insulating
member such that the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt takes a
setting value, the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt can be highly
preciously controlled.

[0089]In order to grow a high-quality silicon single crystal such as a
defect-free crystal, the distance (DPM) between the raw material melt and
the heat insulating member arranged above it is very important. The
reason for this is as follows. First, manufacturing margin for a
defect-free crystal is very narrow, and it needs to be accomplished in
all directions on the crystal plane. Since the temperature gradient
around the crystal varies very much by changing the DPM, the DPM can be
used as a control factor for equalizing the temperature gradient in the
central region and the surrounding region. Furthermore, since the
temperature gradient on the plane varies in the longitudinal direction of
the crystal, the DPM needs to be changed depending on the crystal length
so as to fabricate a defect-free crystal in the entire longitudinal
direction of the crystal.

[0090]Therefore, if the distance between the lower end surface of the heat
insulating member and the surface of the raw material melt is controlled
by the above-mentioned method for controlling the lower end surface of
the heat insulating member and the surface of the raw material melt so as
to manufacture a silicon single crystal, the distance between the lower
end surface of the heat insulating member and the surface of the raw
material melt can be controlled highly precisely, so that the temperature
gradient of the crystal axis in the direction of the crystal growth axis
can be controlled extremely precisely. Consequently, a high-quality
silicon single crystal can be manufactured efficiently and with high
productivity.

[0091]Furthermore, by making the manufactured silicon single crystal
manufactured by the above-mentioned method for manufacturing a silicon
single crystal defect-free on the entire plane in the radial direction,
the defect-free region of the silicon single crystal can be enlarged, so
that manufacturing yield of the silicon single crystal can be further
improved.

[0092]The present invention is described more in detail in reference to
examples of the present invention, though the present invention is not
limited to the examples.

Example 1

[0093]As an apparatus for manufacturing a silicon single crystal, an
apparatus for manufacturing a silicon single crystal 40 shown in FIG. 2
was used.

[0094]First, at a lower end of the heat insulating member 14, a projection
17 and a reference reflector 18 were mounted.

[0095]As the reference reflector 18, a hard and transparent quartz rod of
which tip a white quartz was affixed was used.

[0096]The projection 17 had a length which was shorter than a DPM setting
value while pulling a silicon single crystal 3 and which was longer than
the length of the reference reflector 18, had such a material and a form
that the silicon single crystal was conically cutted and its front
surface was etched and cleaned to be a mirror plane. After mounting the
projection 17, the length of the projection 17 projecting below the heat
insulating member was measured, so that it was confirmed that the length
was shorter than the initial setting DPM at the beginning of pulling a
silicon single crystal by 20 mm.

[0097]First, a quartz crucible 5 having a bore diameter of 800 mm (for
pulling a silicon single crystal having a diameter of 300 mm) was filled
with 340 kg polycrystalline silicon material. After melting the
polycrystalline silicon material by a heater 7, a horizontal magnetic
field having a central magnetic field intensity of 4000 G was applied by
a magnet 16.

[0098]Then the crucible was raised slowly and moved until the projection
17 mounted at the lower end of the heat insulating member 14 was
contacted with a raw material melt 4. The contact of the raw material
melt 4 with the projection 17 was detected by means of a measurement
apparatus 20 by electricity flowing from the heat insulating member 14 to
a crucible axis 15.

[0099]The DPM at the detecting moment was given as DPM setting value--20
mm, and a location R1 of the mirror image of the reference reflector 18
reflected on the surface of the raw material melt was detected by a
fixed-point observing apparatus (camera) 19.

[0100]Next, the crucible was lowered by 20 mm so as to match the location
with the initial location of the surface of the raw material melt at the
beginning of pulling the silicon single crystal. At the same time
conversion factor was determined, too. In other words, a travel distance
B of the mirror image was measured when the crucible was moved by 20 mm
(i.e. a travel distance C of the surface of the raw material melt) so as
to allow the travel distance C of the surface of the raw material melt
while pulling the silicon single crystal to be calculated from the travel
distance B of the mirror image.

[0101]After the setting was thus completed, the silicon single crystal was
pulled. As described above, in order to make a large defect-free crystal
region in the pulled silicon single crystal, the DPM was preferably
varied as needed during manufacturing the crystal. Therefore, the silicon
single crystal 3 was pulled such that the DPM was controlled by a control
apparatus 22 for controlling the crucible location such that the DPM
might take the most preferable pattern.

[0102]The DPM setting values and measurement values of Example 1 are shown
in FIG. 4, while a schematic view illustrating a silicon single crystal
obtained by controlling the DPM as in FIG. 4 is shown in FIG. 5. FIG. 4
is a view showing measured and setting values of the DPM measured by a
DPM measuring method in accordance with the present invention. In order
to read out a subtle change in the DPM in a graph of FIG. 4, the values
in the longitudinal axis in FIG. 4 are those deducting the initial DPM
value at the beginning of pulling the silicon single crystal from the
measured DPM values, while the ratio of the length of the pulled silicon
single crystal in the direction of the growth axis was plotted on the
scale of the horizontal axis.

[0103]From FIG. 4, it is apparent that the DPM could be controlled in the
same way as the DPM setting values. Thereby, it is apparent that a
quality of the crystal pulled by this method is as shown in FIG. 5, and a
silicon single crystal, which is defect-free almost on the entire plane,
could be manufactured.

Example 2

[0104]A silicon single crystal 3 was pulled in the similar way as in
Example 1, other than that the distance between the lower end of the heat
insulating member and the front surface of the raw material melt was
actually measured by using a seed crystal.

[0105]Note that the method of actually measuring a DPM using the seed
crystal was as follows. First lower end of a seed crystal 12 was detected
by an apparatus for detecting a reference location 24 as shown in FIG.
3(b), so that the location was set as a reference location. Then the
lower end of the seed crystal 12 was stopped at a location corresponding
with a desired DPM of the surface of the raw material melt when the
crucible was raised so as to contact with the raw material melt 4. Then
the crucible was raised so as to contact the lower end of the seed
crystal 12 with the raw material melt 4. Based on the distance between
this contact location and the reference location as well as a known
distance between the lower end surface of the heat insulating member and
the reference location, a distance A between the lower end surface of the
heat insulating member and the surface of the raw material melt was
actually measured.

[0106]As the result of controlling the DPM as in Example 2, similar result
shown in Example 1 could be obtained. In other words, the DPM could be
controlled such that the DPM measurement values almost matched with the
setting values similarly in FIG. 4, so that a manufactured silicon single
crystal thus obtained by this method was a silicon single crystal which
was defect-free almost in the entire plane as shown in FIG. 5, similarly
as in Example 1.

Comparative Example

[0107]A silicon single crystal was pulled under the same conditions as in
the Examples except that the DPM was controlled. Here the crucible was
moved up or down by calculating a volume of a quartz crucible 5 from its
inner diameter, by utilizing the fact that the raw material melt was
lowered by the amount corresponding to the weight of the pulled silicon
single crystal, and by raising the crucible for compensating the amount
in the longitudinal direction so as to locate the crucible with the
desired DPM in the longitudinal direction by calculating the DPM.

[0108]The DPM setting values and measurement values of the Comparative
Example are shown in FIG. 6, while a schematic view illustrating a
silicon single crystal obtained by controlling the DPM as in FIG. 6 is
shown in FIG. 7. FIG. 6 is a view showing the DPM setting values and
measurement values measured by a conventional DPM measuring method. It
was apparent as shown in FIG. 6, the DPMs were as a result deviated from
the setting values from the location of the silicon single crystal of
which length was about 20%. The quality of the crystal was as shown in
FIG. 7, and the crystal was a defect-free crystal in the first-half area,
while it was not a defect-free crystal in the latter-half area.

[0109]It was considered that the DPM did not match with the calculated
value because the graphite crucible 6 was degraded. The graphite crucible
6 had a lesser thickness over time. It was considered that the quartz
crucible 5, which was soft at high temperature, was deformed by sticking
to a graphite crucible 6, so that the inner diameter was increased as a
result. Therefore, the lowering amount of the surface of the raw material
melt was assumingly smaller than the calculated value, so that DPM was
narrow than the setting value.

[0110]The present invention is not limited to the embodiments described
above. The above-described embodiments are merely exemplarily in nature,
and any of those having the substantially same constitution as the
technical idea described in the appended claims and providing the similar
working effects are included in the scope of the technical range of the
present invention.